When a computer system is started, e.g., powered on, a process known as “booting” loads program code instructions, such as an operating system image, into the system's memory, so that the system can begin operations. The code instructions can be loaded from a storage device, such as a magnetic disk drive (“HDD”), a solid state disk (“SSD”), a read-only memory, and so on. Solid state disks store data in devices such as Flash memory chips that have no moving parts and are substantially faster to access than hard disks, and systems that use SSD's often perform operations more quickly and responsively than similar systems that use HDD's, which have moving parts and store data at physical locations that are accessed by moving mechanical mechanisms. However, solid state disk (SSD) storage is more expensive than hard disk (HDD) storage, so HDD's can store much more data than similarly-priced SSD's. There is therefore a tradeoff between performance and cost when deciding whether to use an SSD or an HDD.